The present invention relates to a method of forming a thin film for a semiconductor device, and, more particularly, to a plasma-enhanced chemical vapor deposition (CVD) method for forming a thin film on the surface of a body, such as a semiconductor substrate.
One method which has been used to form a thin film on the surface of a body, such as a semiconductor substrate, is the plasma-enhanced chemical vapor deposition (CVD) technique. In this technique, the body is placed in a reaction chamber and a reaction gas is introduced into the chamber. The gas is activated by means of a plasma discharge created in the chamber. This causes the reaction gas to react and deposit a thin film of a material on the surface of the body.
The methods that have been used on a practical basis for the purpose of creating a plasma in a reaction chamber for plasma-enhanced CVD include a method in which an electrical power source with a frequency of 13.56 MHz or 400 KHz, or the like, is applied to a pair of opposed electrodes which are within the reaction chamber. The speed of deposition and the quality of the deposited thin film are controlled by adjusting the power of this electrical power source. Another method of creating the plasma in the reaction chamber uses a microwave radiation of 1.54 GHz which is introduced into the reaction chamber by means of a wave guide. This method is known as ECR plasma CVD. In the plasma enhanced CVD techniques, gases such as tetraethylorthosilicate (TEOS) gas and silane (SiH4) have been used as reaction gases to cause a thin film of SiO or SiON to deposit on the surface of a semiconductor substrate.
With the recent development of high density semiconductor integrated circuit devices (VLSIs), there has been created a crucial need for techniques that can create ultrafine configurations in the submicron range. In order to respond to this demand, the possibility of using conventional techniques to create submicron configurations was considered by conducting an empirical study on the configuration of thin films produced by conventional plasma-enhanced CVD methods.
Referring to FIGS. 1(a) to 1(f), there is shown sectional views of semiconductor devices 10a-10f comprising a substrate 12a-12f having a layer 14a-14f of an insulating material, such as silicon dioxide, on a surface 16a-16f thereof. A plurality of spaced, parallel strips 18a-18f of a conductive material, such as aluminum, are on the insulating layer 14a-14f, and are coated with a layer 20a-20f of an insulating material, such as silicon dioxide. The conductive strips 18a-18f are of different widths with the strip 18a being the widest and the strip 18f being the narrowest. Also, the spacing between the conductive strips 18a-18f vary with the strips 18a being spaced apart the greatest distance and the strips 18f being spaced apart the closest distance. The insulating coatings 20a-20f were formed by a conventional plasma-enhanced CVD (referred to hereinafter as xe2x80x9cPECVDxe2x80x9d) wherein a reaction gas of SiH4 was introduced in a reaction chamber and a plasma was created in the reaction chamber by applying a single 13.56 MHz high-frequency electrical power source between a pair of opposing electrodes in the chamber. As can be seen in FIGS. 1(a) to 1(f), the sides of the silicon dioxide coating 20a-20f have a cross-sectional configuration formed so as to posses roundness in the form of protrusions. More specifically, the thin film 20a-20f near the upper side of the aluminum strip 18a-18f is thicker than the portion of the coating 20a-20f near the bottom of the aluminum strip 18a-18f. This results in the problem of gaps being created near the bottom of the aluminum strips 18a-18f. This is especially serious in high-density strips (wiring) on the submicron level, where the gap spacing between the aluminum strips is reduced as shown in FIGS. 1(e) and 1(f).
Referring to FIGS. 2A to 2F, there are shown sectional views of a semiconductor device 22a-22f which is similar to the semiconductor device 10a-10f of FIGS. 1A to 1F. The semiconductor device 22a-22f comprises a substrate 24a-24f of a semiconductor material, such as silicon, having a layer 26a-26f of an insulating material, such as silicon dioxide, on a surface 28a-28f thereof. A plurality of spaced, parallel strips 30a-30f of a conductive material, such as aluminum, are on the insulating layer 26a-26f. The conductive strips 30a-30f are coated with a layer 32a-32f of an insulating material, such as silicon dioxide. The conductive strips 30a-30f are of different widths, with the conductive strip 30a being the widest and the conductive strip 30f being the narrowest. Also, the spacing between the conductive strips 30a-30f varies with the conductive strips 30a being spaced apart the greatest distance and the conductive strips 30f being spaced apart the least distance.
The insulating coatings 32a-32f were formed by PECVD using tetraethylorthosilicate (TEOS) as the reaction gas. The plasma was created in the reaction chamber by simultaneously applying a 13.56 MHz high-frequency electrical power source and a 400 kHz low-frequency electrical power source between opposing electrodes in the chamber. When these electrical power sources of two frequencies are utilized, it is possible to enhance the quality of the thin film and the speed with which it is created.
As can be seen from FIGS. 2A to 2F, the configuration of the sidewalls of the silicon dioxide thin film 32a-32f has little or no curvature when compared to the configuration of the silicon dioxide thin films 20a-20f shown in FIGS. 1A to 1F. Thus, this technique can be said to make a major contribution to enhancing the control of the formed thin film. However, as is shown in FIGS. 5(e) and 5(f), the reduction in the gaps is insufficient in the creation of high density thin films in the submicron range at which the distance between the aluminum strips 30e and 30f decreases. Also, it is difficult with the above conventional techniques to respond to the demand for the creating of higher densities. Therefore, it is desirable to have a method of depositing a thin film for a semiconductor device than will provide good coatings even with high density devices.
The present invention is directed to a method of forming a thin film on a substrate of a semiconductor device wherein the substrate is subjected to a mixture of tetraethylorthosilicate gas and a halogen gas, and a plasma is formed by means of a plurality of electrical power sources of different frequencies.
Viewed from another aspect, the present invention is directed to a method of forming a thin film on a substrate of a semiconductor device wherein the substrate is placed within a reaction chamber and a plasma is created in the chamber by means of a plurality of electrical power sources of different frequencies. A reaction gas is introduced into the reaction chamber and subjected to the plasma to cause the gas to react and deposit a layer on the substrate. The reaction gas is a mixture of tetraethylorthosilicate gas and a halogen gas.